For commercial aircraft, it is important in emergency situations to be able to quickly and effectively evacuate all passengers. In support of this, various aircraft components must be operable, even if the aircraft loses its ability to provide electrical and/or hydraulic power.
One example of where this is crucial is in the retraction of wing spoilers. During an emergency, overwing exit doors may be opened to provide passengers with an alternative escape route. It is typical for the opening of these doors to trigger automatic deployment of self-inflating overwing escape slides. Because these slides are puncturable, it is important to quickly retract any extended wing surfaces that may interfere with or damage the slides, or that may interfere with passenger egress. Should the aircraft lose its hydraulic and/or electrical systems, some type of backup system must be available to retract these surfaces.
FIG. 1 illustrates a known aircraft having an actuator 10 that is activated by a pyrotechnic device 12. The opening of an overwing escape door triggers a battery to send a current to the pyrotechnic device and to an electrical relay that removes power from a hydraulic servo valve that is mechanically biased to the retract position with power off. The device, in turn, causes an actuator piston 14 to mechanically rotate a spoiler panel 16 to its stowed position. This system works satisfactorily, but has a number of implementation disadvantages. One disadvantage is that the actuator must be connected to wing structure that is capable of withstanding the actuator's reaction loads when fired. This requires an increase in the thickness of the wing loading members, which adds undesirable weight to the wing. A second disadvantage is that the spoiler surface must be designed to include a moment arm for the actuator to react against. This adds weight to the spoiler surface and makes the configuration no longer compatible with other variations of that particular airplane model. A third disadvantage is that the actuator must be mounted in a specific location to push against the spoiler surface.
A fourth disadvantage is that the actuator is not connected to the main hydraulic system. Therefore, the actuator must be checked periodically for leaks, and if leaks have occurred, they must be repaired and the actuator manually refilled with hydraulic fluid. In addition, once the actuator is fired, it must be manually repositioned to its initial state. Should an anomalous firing occur in flight, the actuator would apply a load to the spoiler surface until the gas pressure is manually released, on the ground.
U.S. Pat. No. 5,582,010 describes a pyrotechnically operated pressurization device attached directly to a hydraulic tank. The device is activated by an electronic igniting unit that heats a combustion chamber filled with a propellant charge. The expanding propellant charge activates a cartridge base to eventually force excess hydraulic fluid into the tank. Upon activating the device, the entire hydraulic tank and its corresponding circuits are pressurized. A disadvantage of this device is the possibility that the pressurization may be insufficient for the entire hydraulic system, plus any leaks or pressure outlets resulting from the emergency situation may thwart the pressurization provided by the pyrotechnic device.
Thus, a need exists for an auxiliary hydraulic power system capable of providing emergency hydraulic fluid pressurization to select aircraft components. Example components that would benefit from such a device are wing spoilers. An ideal auxiliary spoiler retract system would be capable of quickly retracting extended spoilers upon the opening of overwing exit doors and/or deployment of overwing emergency escape slides. The ideal auxiliary spoiler retract system would be pyrotechnically activated, would include components that do not require significant maintenance, and would have minimal impact on the aircraft's main hydraulic system. Activation of the system would provide immediate hydraulic pressure to the spoilers without necessarily having to provide pressure to the entire hydraulic system. Further, the ideal auxiliary hydraulic power system would be available regardless of the availability of the aircraft's main electrical and/or hydraulic systems. The present invention is directed to fulfilling these needs.